How to sum and count in grouping in sql - sql

Question

I have tables like below.
I would like to grouping and counting by referreing to its score.
customer score
A 10
A 20
B 30
B 40
C 50
C 60
First, I would like to sum score by customer
It achived by group by method.
customer score
A 30
B 70
C 110
second, I would like to count by binning following band.
I couldn't figure out how to count after grouping
band count
0-50 1
50-100 1
100- 0
Are there any way to achieve this?
Thanks

Answer 1

You could use a union approach:
WITH cte AS (
SELECT COUNT(*) AS score
FROM yourTable
GROUP BY customer
)
SELECT '0-50' AS band, COUNT(*) AS count, 0 AS position FROM cte WHERE score <= 50 UNION ALL
SELECT '50-100', COUNT(*), 1 FROM cte WHERE score > 50 AND score <= 100 UNION ALL
SELECT '100-', COUNT(*), 2 FROM cte WHERE score > 100
ORDER BY position;

Answer 2

Try the following with case expression
select
case
when score >= 0 and score <= 50 then '0-50'
when score >= 50 and score <= 100 then '50-100'
when score >= 100 then '100-'
end as band,
count(*) as count
from
(
select
customer,
sum(score) as score
from myTable
group by
customer
) val
group by
case
when score >= 0 and score <= 50 then '0-50'
when score >= 50 and score <= 100 then '50-100'
when score >= 100 then '100-'
end

Answer 3

I would recommend two levels of aggregation but with a left join:
select b.band, count(c.customer)
from (select 0 as lo, 50 as hi, '0-50' as band from dual union all
select 50 as lo, 100 as hi, '50-100' as band from dual union all
select 100 as lo, null as hi, '100+' as band from dual
) b left join
(select customer, sum(score) as score
from myTable
group by customer
) c
on c.score >= b.lo and
(c.score < b.hi or b.hi is null)
group by b.band;
This structure also suggests that the bands can be stored in a separate reference table. That can be quite handy, if you intend to reuse these across different queries or over time.